The present invention relates to a method and system for processing (producing) a semi-conductor device, and particularly to a technique for improving the accuracy of overlay at the mix-and-match exposure process in which different exposure tools are used for different layers on a semiconductor substrate.
In the recent trends of higher integration and enhanced functioning of semiconductor devices, the production process is required to be much more accurate for accomplishing these demands. On the other hand, reduction of the production cost of semiconductor devices is another crucial subject.
In the production process of a semiconductor device, circuit patterns formed on exposure masks (will be termed simply “masks”) are transferred on to a semiconductor wafer (will be termed simply “wafer”) which is coated with photo-resist by using a projection exposure tool (apparatus). As a semiconductor device is made circuit patterns on multiple layers, the circuit pattern of one layer is performed an exposure process, i.e., an overlap exposure process on to the circuit pattern of the lower layer in the state of that the circuit pattern of one layer is registered to the circuit pattern of the lower layer.
The production line of semiconductor devices has the installation of multiple projection exposure tools in general, and there exists the disparity of accuracy among these projection exposure tools. On this account, when the mix-and-match exposure, the so-called overlap exposure is carried out among multiple exposure tools, the disparity of accuracy among the exposure tools is generated error among layers called “matching error” in a product of the semiconductor device.
A scheme of preventing the matching error is using the same projection exposure tool throughout all steps of semiconductor device production process; however, it results in a lower operation efficiency of projection exposure tools and increased production cost.
Although the mix-and-match exposure has limited applications that allow certain ranges of matching error, the expansion of its application is demanded strongly from the viewpoint of cost reduction. Therefore, it is a crucial technique to correct the matching error in carrying out the mix-and-match exposure.
Japanese patent publication No. Hei 7-211627 discloses a method of optimized overlap exposure, which is based on the formulation of aberration curves of lenses of projection exposure tools in approximate functions, the calculation of correction factors from the disparity of functions, and the correction of exposure condition.
Another Japanese patent publication No. Hei 9-82607 discloses an exposure method which is based on the correction of the overlay measurement result at exposure by using distortion data of objective lens in each of machining numbers of each exposure tool, and the adjustment of the projection magnification factor and the rotation of the projected image.
Both of the above-mentioned prior arts are intended to correct the entire exposure field of the exposure tools.
However, in the trends of higher integration and enhanced functioning of semiconductor devices, when the mix-and-match exposure is attempted without the investment for a huge facility providing many exposure tools in the production line of semiconductor devices, it is becoming difficult to keep the matching error within the allowable range throughout the entire exposure field.
What is crucial for semiconductor device products is the accuracy of overlay in the device area (area where circuit patterns for constructing semiconductor device are formed) where is smaller than the exposure field. The above-mentioned prior arts do not consider this affair.